Ion-Induced Nucleation: The Importance of Chemistry

Experiments have shown that ions can substantially increase vapor-to-liquid nucleation rates. However, interpretation of these experiments is complicated by ambiguities arising from the manner in which the ions are produced. Several studies have concluded that water has a general preference for anions over cations. We show that specification of the ion’s sign alone is insufficient to provide an understanding of the aqueous ionic cluster thermodynamics and that classical ion-induced nucleation theory does not treat the cluster physics properly to describe ion-induced nucleation accurately.

Figure 1

Aqueous ionic cluster chemical potentials at $T=243\mathrm{K}$: $X_{\mathrm{SM}}^{-}({\mathrm{H}}_2\mathrm{O}{)}_i$ (open triangles), $X_{\mathrm{SM}}^{+}({\mathrm{H}}_2\mathrm{O}{)}_i$ (solid triangles), $X_{\mathrm{LG}}^{-}({\mathrm{H}}_2\mathrm{O}{)}_i$ (open squares), $X_{\mathrm{LG}}^{+}({\mathrm{H}}_2\mathrm{O}{)}_i$ (solid squares), $({\mathrm{H}}_2\mathrm{O}{)}_i$ (solid circles), CNT pure water (solid line), CIINT with ion radius $r_X=0.1\AA$ (small-dashed curve), CIINT with ion radius $r_X=10\AA$ (large-dashed curve). The insert provides an expanded view of the larger clusters.